It is known that diamond films can be readily produced by chemical vapor deposition (CVD). See, for instance, J. C. Angus et al., Annual Review of Materials Science, Vol. 21, p. 221 (1991), incorporated herein by reference.
Diamond is not only the hardest known substance but also has the i highest elastic modulus, highest atomic density, highest Debye temperature, and highest room temperature thermal conductance. It is chemically inert and highly transparent from the ultraviolet to the infrared. Furthermore, diamond is a wide gap semiconductor that may be useful for high temperature and/or high voltage device applications. Because of these and other properties, diamond films are of interest for applications such as heat spreaders, optical windows, X-ray lithography, low-friction or wear-resistant surfaces, cuting tool coatings, and active electronic device elements.
For many applications it will be necessary to remove material from a diamond film. For instance, currently available CVD diamond films typically exhibit a roughly cone-shaped columnar structure, with relatively fine-grained material near the bottom of the film, and relatively large-grained faceted material near the top. (See, for instance, FIGS. 1.16(a) and (b) of "Properties and Applications of Diamond", J. and E. Wilks, Butterworth Heinemann Ltd, 1991, p. 24.) Exemplarily, films of thickness of order 200 .mu.m frequently exhibit variations in height of the top surface of order 20-60 .mu.m. A strongly faceted surface with significant height variations is clearly undesirable for, e.g., an optical window or a heat spreader. Thus, techniques for removing material from a diamond film are required.
Because of the extreme hardness of diamond, mechanical polishing or thinning of a CVD diamond film is time consuming and costly. Polishing by reaction with oxygen ions or gas tends to cause undesirable grain boundary etching and pitting. Other removal techniques such as laser ablation, Ar ion beam irradiation, and electrical discharge have been reported but have not proven fully satisfactory. See, for instance, "Properties and Applications of Diamond", op. cit., especially pp. 259-263.
It is known that diamond grinding wheels perform relatively poorly when used to grind hard steel. This has been attributed to graphitization of diamond particles of the grit. It has been suggested that the thus produced graphite is removed from the grit by abrasion rather than by diffusion into the steel. Ibid, pp. 456-458. See also p. 264 of the same monograph, where the authors suggest (because diamond wears at " . . . quite an appreciable rate when rubbed on ferrous metals . . . ") that it should be possible to polish a diamond by rubbing at high speed with a steel or cast-iron wheel, but proceed to point out that in actual fact this process typically is very slow compared to normal rates of polishing. See, however, M. Yoshikawa, The International Society for Optical Engineering, (SPIE) Vol. 1325, "Diamond Optics III", A. Feldman et al., editors, 1990, p. 210, wherein polishing of polycrystalline diamond film by means of iron and nickel polishing wheels is reported, at temperatures in the range 750-950.degree. C., in vacuum, H.sub.2, He, Ar and N.sub.2. See also T. P. Thorpe et al., ibid p. 230, who disclose polishing of polycrystalline diamond film by means of an iron polishing wheel at 650-850.degree. C. in flowing H.sub.2, and A. B. Harker et al., ibid p. 222, who have lapped polycrystalline diamond films on an iron plate at 730-900.degree. C. in H.sub.2.
The above described polishing and lapping techniques cannot be used to pattern a diamond film, and may at times be impractical if removal of a substantial amount of material is desired.
On page 264 of the monograph by J. and E. Wilks can be found a review of earlier work (A. P. Grigoriev et al., Indiagua, Vol. 39(3), pp. 47-54, 1984), which reads as follows:
"A different way of working diamond with metal has been described by Grigoriev and Kovalsky (1984). The principle of their method is shown in FIG. 9.34. A piece of iron or nickel foil is cut to shape and placed on the surface of the diamond which is then heated to about 1000.degree. C. in an atmosphere of hydrogen. At this temperature the carbon atoms in contact with the lower surface of the foil diffuse through the foil to the top surface where they react with the hydrogen and are carried away as methane. Hence the foil sinks into the diamond as shown, engraving its shape on the surface. The authors describe variants of this method which they have developed for various purposes including sawing and drilling."
From the above quote and FIG. 9.34 of the monograph it is clear that the prior art method was used on a single crystal of diamond and not on polycrystalline film.
From the above discussion it will be apparent that the art does not yet possess a fully satisfactory technique for removing material from a diamond film. Thus, it would be highly desirable to have available a simple, inexpensive and efficient technique for removing material from a (polycrystalline) diamond film, that is free of some of the limitations of prior art techniques. This application discloses such a technique.